Heat exchangers are used in various capacities in automotive applications. For example, all automobiles have water cooled engines and employ a radiator and a heater core. Automobiles equipped with air conditioning also include an evaporator and a condenser. These heat exchangers are made from aluminum and consist of two spaced header tanks interconnected by flow tubes having cooling fins extending therefrom. Fluid is circulated through the header tanks and flow tubes to effect the necessary temperature drop.
The header tanks, flow tubes, and cooling fins are rigidly attached to one another by brazing. It has been found that this brazing operation can be most efficiently accomplished in a furnace for mass production applications. These furnaces are elongated members through which heat exchangers are conveyed in a continuous stream. It has been found that superior braze results can be obtained when the atmosphere within the braze furnace is evacuated of oxygen. In its place, an inert gas, i.e., inert to the heat exchangers, braze, flux, and all other internal components of the braze furnace, it established within the braze furnace. Hence, as the workpart travels through the braze furnace, its temperature is raised to the braze liquification temperature and back down to a braze solidification temperature all within an oxygen free controlled atmosphere.
Even a small amount of oxygen present in the braze furnace will have a significantly harmful effect on the braze joint. Hence, great care is taken to seal the exterior of the housing from cracks and leaks occurring therein which would tend to allow oxygen infiltration into the braze chamber. Although this is possible in theory, in application thermal expansion and contraction caused by the extreme temperatures generated within the braze furnace inevitably create cracks in the housing which permit oxygen infiltration into the braze chamber.
Examples of prior art braze furnaces may be found in U.S. Pat. No. 3,756,489 to Chartet, issued Sep. 4, 1973, U.S. Pat. No. 3,882,596 to Kendziora et al, issued May 13, 1975, and U.S. Pat. No. 4,501,387 to Hoyer, issued Feb. 26, 1985. These references all disclose braze furnace assemblies susceptible to oxygen infiltration into the braze chamber in the event a crack or opening occurs in the housing.